1. Field of the Invention
The present invention relates to a vapor-compression type refrigerant cycle system in which expansion energy in an expansion unit is recovered. The present invention is suitably applied to a refrigerant cycle system in which refrigerant such as ethylene, ethane, nitrogen oxide, or carbon dioxide is used so that pressure of refrigerant discharged from a compressor exceeds critical pressure.
2. Description of Related Art
In a conventional vapor-compression type refrigerant cycle, after compressed refrigerant is cooled and is press-reduced, low-pressure refrigerant is evaporated in an evaporator so that refrigerating effect is obtained. However, in the conventional refrigerant cycle, the refrigerating effect is determined based on an enthalpy difference of refrigerant between an inlet side and an outlet side of the evaporator. Therefore, when temperature within the evaporator increases and pressure within the evaporator (i.e., pressure at a refrigerant inlet of the evaporator) increases, the enthalpy difference of refrigerant between the inlet side and the outlet side of the evaporator becomes smaller, and the refrigerating effect of the refrigerant cycle decreases.